How can I change blender´s 2.78 splash screen?
I have meanwhile solved this one. The key is to rerun Cmake once you have modified the splash.png and splash_2x.png files. Cmake is where the conversion of the files happens. And that's why nothing happens when you just modify the files.

So modify the png files, clear cache in Cmake, configure in Cmake, generate in Cmake, then compile again.